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<div>In the Pacific Northwest, root-knot nematodes (<i>Meloidogyne spp</i>.) are a serious problem on potatoes. There is a critical need to reduce the use of toxic chemicals in nematode management. In order to develop the tools for engineering nematode resistance in potato, we must first understand the molecular components of plant defense and the nematode strategies used to overcome these defenses. During infection, the nematode secretes molecules called effectors. The effectors suppress plant defenses and/or alter the host physiology to enable successful nematode infections. Our lab studies root-knot nematode effectors, and we identified a novel effector called Mh265. Plants that ectopically express Mh265 were more susceptible to nematode infection. Interestingly, Arabidopsis that expressed Mh265 exhibited a suppression of elicitor-induced callose deposition. We concluded that Mh265 is secreted by the nematode in order to modulate basal plant immunity. In addition to effectors, our group is also interested in plant immune responses during nematode infections, and in particular, we have focused on the role of the defense hormone jasmonic acid (JA). Using several mutants in JA biosynthesis/perception, we were the first to find that a jasmonic acid precursor called OPDA acts as a defense-signaling molecule in the plant-nematode interaction. This result has given us insights into the mechanisms regulating plant defenses against nematodes. <p> </div>